Compilare: main.cpp: In function 'void check()': main.cpp:12:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::stack<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 12 | for (int i=0; i<d.size() && ok; ++i) { | ~^~~~~~~~~ main.cpp: In function 'void solve(std::string&)': main.cpp:33:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 33 | for (int i=0; i<s.size(); ++i) { | ~^~~~~~~~~